Sintering of endothermic materials



Oct. 10, 1961 K. MEYER ETAL 3,003,863

SIN'I'ERING 0F ENDOTHERMIC MATERIALS Filed Oct. 25, 1958 Fig. 1

Invenfors KM T M E Y I bfl/V #1701614 5 j 6 l g 5'4 at/vays United state Patent 1 Filed Oct. 23, 1958, Ser. No. 769,128 Claims priority, application Germany Nov. 5,

1 Claim. (Cl. 75-5) This invention relates to sintering and, in particular, to the sintering'of endothermic materials.

In the sintering of endothermic materials on a sinter grate or band, as in the sintering of iron ores, it is known to supply the heat by the simultaneous use of solid fuels and hot gases. Moreover, it has been established that with the use of mixed solid and gaseous fuels the fuel efficiency is greater than that obtained with the use of solid fuels only and that the fuel efficiency in using gases alone is much lower than with the use of solid fuel alone. i

Generally in sintering processes, especially at the sintering of iron ores, amelting zone is formed in the sinter bed. In this zone there is the sinter mixture in a doughy condition which is necessary to bring the material to be sintered in the desired condition. Because of its doughy band is not reduced. On the. other hand it can be insured that, by the suitable regulating of the temperatures of the hot gases in the various parts of the hood such a quantity of calories are brought therein, that a considercondition the melting zone has a certain resistance to I the gases to be drawn through. The resistance is the greater the thicker the melting zone is. Therefore it is desired to keep the melting zone not greater than necessary so that the gas passage is not restrained too much. A great gas passage is desired to promote the combustion and the other processes in the sinter bed and thereby to result a rather great efficiency and production of the sinter apparatus.

The object of this invention is to obtain a greater efliciency in the use of gaseous fuel in the heat treatment of endothermic materials.

It has been discovered in this invention that in a bed of endothermic material mixed with solid fuel and with simultaneous use of gaseous fuel and which is burned on a sinter band the decrease in the efficiency of the use of gaseous fuels has, for one of its reasons, the fact that during the burning of the solid fuel together with the heat from the hot gases the melting zone is increased. The hot gases tend to make the melting zone of greater thickness than would occur in the use of solid fuel alone, and this zone of greater thickness stops the passage of the hot gases through the bed and thus also slows the sinter process and the velocity of the sinter band, and the sinter production is decreased. Thus the efiiciency of the sinter band is reduced. The reason for this fact is that in the first part of the sinter process hot gases containing oxygen are led air which is usually drawn through.

According to this invention, the extent of the thickness of this melting zone is kept as thin as possible by subjecting the bed of material to hot gases of successively varying temperatures. Preferably, immediately after feeding the sinter band with the sinter mixture, hot gases at about 1000" C. are drawn through the bed in order to ignite the solid fuel in the bed. Immediately thereafter, gas at a lower temperature is drawn through the bed in order to create in the sinter bed above the melting a zone of somewhat lower temperature. If desirable, by using several times alternatively of higher and lower temperatures, various successive layers of various temperature can be created in series.

The result is that an excessive thickness of the melting zone is not caused by the drawing of hot gases through the sinter bed with the simultaneous burning of the solid fuel in the bed and thus the production of the sinter to the sinter bed instead of the cool able part of the entire heat requirement for the sintering bed will be supplied by the hot gases drawn through the slnter bed. i

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic cross-sectional view of a sinter apparatus according to the prior art;

FIGUREla is a detail view of the sinter bed exagger-ated in vertical scale;

FIGURE 2 'is a schematic cross-sectional view of a sinter apparatus according to this invent-ion; and.

FIGURE 2a is an enlarged detail view of FIGURE 2 exaggerated in vertical scale.

The sinter apparatus has a continuous grateor band 1 upon which is placed a protective layer of material 2. The material to be sintered is formed as a bed 3 upon layer 2. The gas for igniting the solid fuel in bed 3 is drawn from hood '4 through the sinter bed. "Additional hot gases are supplied through hoods 5 and 6.

As an example of this invention, the bed 3 is composed of 40 parts recycled pyrites, 10 parts blast furnace dust, 20 parts magnetite concentrates, 8 parts pelletized mill dust, 22 parts purple ferric oxide ore, 25 parts recycled material and 7.5 parts coke fines. Hot gas at a temperature of about 1000 C. is drawn through the bed 3 from the hood 4. If the gas supplied from hoods 5 and 6 were at the same temperature as the gas from hood 4, then a melting zone a would be formed in bed 3. However, according to this invention, a gas at a lower temperature, such as 800 C., is drawn through the bed from hood 5 and, as shown in FIGURES 2 and 2a, the melting zone b is formed of less thickness than zone a of FIGURE la. A hotter gas having a temperature higher of that in hood 5, such as 900 C., is drawn from hood 6 through bed 3 and forms a zone 0 as a layer overlying zone 11. This zone 0 has a temperature less than that of the melting temperature in zone b, but allows sufficient heat to be drawn through the bed to maintain melting zone b.

The temperatures given in the above example can be raised or lowered depending upon the particular characteristics of the raw material being heat treated. The heat supplied by the hot gases should not be great enough to increase the width of melting zone b. The temperatures of the gases drawn from the hood following the first ignition hood are kept as high as possible but below the point which would cause a widening of the melting zone.

EXAMPLE 1 Conventional sintering On a sinter machine with a sintering area of m. (2.50 meter width, 30 meter length) a steel iron sinter mixture was sintered. The composition of the sinter mixture was as follows:

Parts Ore with a moisture content of 8 percent and a loss on ignition of 11.3 percent Recycled materi l 32 Coke fin 8.3

With a heating value of 5200 calories per kg.

ating value of the blast furnace gas was 900 calories r normal cubic meter. The sinter output in this conntional process was 75 tons per hour. The consumpn of coke was 101.9 kg. per ton sinter=530,000 calo- =s per ton sinter and the blast furnace gas consumpn for the ignition was 32.4 normal cubic meters per 1 sinter=29,200 calories per ton. The whole consumpln was 559,200 calories.

EXAMPLE 2 Over the same sinter band a second hood for the nultaneous application of hot gases and solid fuel was ilt adjoining to the ignition hood. Both the hoods gether covered 35 percent of the sinter hand area. The :ond hood was divided in three sections. According the conventional art in the whole hood-just as in e ignition hood-a temperature of 1100 C. was mainned. Again the same steel-iron sinter mixture was :ated. The recycled material was the same. The coke dition, however, was reduced to 4.9 parts for 100 parts e mixture. The consumption of gas in the heating od including ignition hood was now 9400 normal bic meters per hour. The quality of the sinter so oduced corresponded to the sinter of the Example 1. to output of the sinter band, however, decreased to .6 tons per sinter per hour. The consumption of coke r ton of sinter was 60.1 kg.=3l2,500 k-ilo calories; the ast furnace gas consumption was 148 normal cubic eters=133,200 kilo calories. Thus the whole consump- I11 was 445,700 kilo calories. The consumption of calo- :s was 20.3 percent lower than in Example 1. At the me time, however, a decrease of the output of 15.2 rcent took place in comparison to Example 1.

EXAMPLE 3 In a third test the temperature was regulated in the iition and the following hood according to the invenn as follows:

The ore mixture again was iron ore sinter mixture the same composition as in Examples 1 and 2. Also e return material charge amounted to about 32 percent. The coke addition was 5 parts of coke fines for parts of ore. The blast furnace gas consumption was 9180 normal cubic meters per hour. With the regulation of temperature as described above the output of the sinter band was 74.5 tons sinter per hour. It corresponds practically to the output of Example 1. The consumption of coke fines was now 61.4 kg. per ton sinter=319,000 kilo calories pef 'ton sinter in the same order of magnitude as in Example 2. The blast furnace gas consumption was 123.2 normal cubic meters per ton sinter=111,000 kilo calories. The Whole heat consumption was 430,000 kilo calories. The consumption of the fuel was 21.3 percent lower than in Example 1. The quality of the sinter corresponded to Example 1.

Having now described the means by which the objects of the invention are obtained.

We claim:

A process for the endothermic treatment of material moving horizontally on a sinter apparatus comprising forming a bed composed of a mixture of the material and solid fuel on said sinter apparatus, drawing hot gas through the bed to ignite the solid fuel and supply additional heat to said bed and thereby form a melting zone of the material in the bed, then drawing a gas cooler than said hot gas through said melting zone in said bed in quantities sufficient to limit an increase in the width of said melting zone and to maintain a thin gas permeable zone in advance of said melting zone and below melting temperature with said cooler gas being hot enough to supply sensible heat to said sinter bed, and then drawing another hot gas at a temperature higher than said cooler gas through said bed for forming a second zone at a temperature less than that of said melting zone but greater than that of thin gas permeable zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,235,261 Labbe Mar. 19, 1941 2,380,056 Lloyd July 10, 1945 2,441,383 Babb May 11, 1948 2,498,766 Pettigrew Feb. 28, 1950 2,750,274 Lellep June 12, 1956 FOREIGN PATENTS 573,539 Great Britain Nov. 26, 1945 720,302 Great Britain Dec. 15, 1954 

